Constant torque hydraulic pump

ABSTRACT

A constant torque hydraulic pump having a swashplate of variable inclination pivotally mounted on a support and rotatable about a predetermined axis. The hydraulic control piston is mounted within the support for modifying the inclination of the swashplate, and a regulating valve is in fluid communication with an outlet orifice of the pump and is coaxially located with respect to the axis. A calibrated orifice assembly is located adjacent to the swashplate, and a spring bearing is located between the regulating valve and the calibrated orifice assembly for enabling inclination of the swashplate in accordance with the pressure at the outlet orifice to maintain a substantially constant driving torque for the pump.

United States Patent [72] Inventor Gerard Leduc 84 bis, rue d'Alsace, Saint-Die, France [21] Appl. No. 796,795 [22] Filed Feb. 5, 1969 [45] Patented Apr. 20, 1971 [32] Priority Feb. 7, 1968 [33] France [31] 138,941

[54] CONSTANT TORQUE HYDRAULIC PUMP 9 Claims, 3 Drawing Figs.

[52] US. Cl 417/218, 7 91/506 [51] Int. Cl F0lb 3/00, F0lb 13/04, F04b 49/00 [50] Field of Search 103/38, 11.14, 161 (a), 162 (a);230/l86, 20

[56] References Cited UNITED STATES PATENTS 2,283,321 5/1942 Doe et al. 103/162 2,915,985 12/1959 Budzich.... 103/162 3,010,403 11/1961 Zubaty 103/173 3,067,693 11/1962 Lambeck 103/161 Primary ExaminerWilliam L. Freeh AttorneyFinnegan, Henderson & Farabow ABSTRACT: A constant torque hydraulic pump having a swashplate of variable inclination pivotally mounted on a support and rotatable about a predetermined axis. The hydraulic control piston is mounted within the support for modifying the inclination of the swashplate, and a regulating valve is in fluid communication with an outlet orifice of the pump and is coaxially located with respect to the axis. A calibrated orifice assembly is located adjacent to the swashplate, and a spring bearing is located between the regulating valve and the calibrated orifice assembly for enabling inclination of the swashplate in accordance with the pressure at the outlet orifice to maintain a substantially constant driving torque for the pump.

PATENTED APR 20 197i sum 1 or 2 CQNS'HANT rononn nrnnttc an The present invention relates to a hydraulic pump comprising an internal control member such that the driving torque of the pump remains constant.

Such a pump is particularly advantageous when it is coupled firstly to a heat engine, which drives it and secondly to a jack which it supplies and which is subject to variable forces, thus for example a jack actuating the arm of an excavating shovel. if the resistance of the earth increases, the pressure necessary in the jack increases, and thus the delivery pressure of the pump and consequently the torque necessary for driving the pump; since the conventional internal combustion engine is only able to supply a maximum torque, it is essential for the pump to be equipped with a regulating arrangement so that the driving torque of the pump can never be greater than that which the engine is able to deliver. its the conventional internal combustion engine is equipped with a regulator which is sensitive to the variations in the number of revolutions per minute and not to the variations of the engine torque, it follows that there are sudden jerking movements in the operation of the installation comprising jack, pump and engine; these sudden jerks are eliminated or at least greatly reduced if the pump is a self-regulating pump necessitating a constant driving torque.

In US. Pat. No. 3,376,822 entitled Variable Delivery Hydraulic Pump," there is described a pump with a swashplate comprising means for causing the inclination of the said plate be be varied under the effect of a pressure originating from any appropriate regulating member.

The present invention relates to a pump of this type, comprising means enabling the inclination of the swashplate to be varied in accordance with a law, such that the driving torque of the said plate remains constant.

By way of example, and in order to facilitate understanding of the invention, reference is made to the accompanying drawing, wherein:

Flt l is a longitudinal sectional view of a pump according to the present invention.

FIG. 2 is a cross section along BB of HG. l;

H6. 3 is a view to a larger scale showing a detail of FIG. ll.

Referring to H6. 1, it is seen that the body of the pump is formed of two parts l and 2. A first plurality of pistons 3 slide in cylinders d, drilled in the body 2, and are supported by springs 5. The cylinder bores d are connected in known manner to an outlet orifice 29, with interposition for each bore i of a nonreturn valve l'. Rotating in the other part 1 of the pump body, by means of roller bearing s, is a shaft 7 which is fast with an element h serving as support for a swashplate it, mounted on the said support 8 by means of a pivot lb.

The support h and the swashplate rotate in a chamber 30 connected to the tank by the orifice Lida.

Formed inside the support d is a cylinder it, in which slides a hollow hydraulic control piston R2. The spherical head 16 of the piston l2 bears against the rear face db of the swashplate by means of a movable contact block l7 as known per se. The spherical head to of the piston i2 is held in contact with the block 17 by means ofaspring M.

A second piston 22 of small diameter slides in a cylinder 21 formed in an element l fast with the part 2 of the pump body; and the spherical head of said piston bears against the fore face he of the swashplate 9, by means of a movable contract block as known per se.

The pistons l2 and 22 are coaxial with the shaft 7 and communicate with one another through the plate 9 by means of a drilled passage W.

Referring to MG. 3, there is shown a calibrated orifice assembly that includes an annular chamber lb and then an annular calibrated passage Rh disposed to the rear of the cylindrical bore 2t, which servm to guide the piston 22; extending through the piston 22 is a conduit 23 which opens into the annular chamber id.

The piston 22 is supported by a spring bearing 24 which bears on a dished member 25, against which rests the rear end of the piston 22.

The spring 24 is disposed inside a cylindrical bore 26 which is formed inside the part 2 of the pump body.

Disposed at the lower end of the said bore 26 is a regulating valve 26), of which the valve member 27 is held at one end by the spring 24 and at the other end by a spring 28.

The valve 20 is connected to the outlet pressure by a passage M. This pressure is directed inside the valve 20, firstly to the rear of the valve member 27 and secondly to an orifice 32. When the system is in equilibrium, which is the position shown in FIG. l, the valve member 27 closes the passage 32 for admission of pressure and also the return passage 33 to the tank, and depending on the direction of its movements, it uncovers one or other of these orifices.

The operation of the pump as thus described is as follows: when the pressure in 29 increases, for example, under the effect of a considerable force of the operating jack (not shown), the pressure at the rear end of the valve member 27 increases and this latter is displaced upwardly, thereby opening the communication between the orifices 32 ad 3%. The pressure arrives by way of the passages 35 and 35, passing through the valve as, the purpose of which will hereinafter be described, and reaching the bore 26. From the latter, the pressure is directed through the calibrated orifice 1d, the chamber 18, the conduit 33, the drilled bore 19 and the drilled bore 13 to the interior of the piston 12.

This pressure forces back the piston which, like the piston described in US. Pat. No. 3, 376, 822, forces back the swashplate 9, this reducing the delivery output of the pump. The pressure acting on the piston 12 is a practically constant fraction of the delivery pressure, and consequently the pressure drop caused by the calibrated passage 18 is shown by an increase in the pressure upstream of the said passage in, this increase in pressure braking the opening movement of the valve member 27, and this has the effect of making the opening of the valve sensitive to the speed of displacement of the plate 9 and thus of stabilizing the system and avoiding the instability phenomena which are due to overcompensation effects.

The purpose of the spring 24 is to stop forcing back the valve member 27, in order to return it to its balanced position when the flow passing through the calibrated passage 18' tends toward zero.

If the delivery pressure obtaining at 29 is called P and if the angle which the face 9a of the plate 9 forms in relation to its axis of rotation is called a the driving torque C of the pump is given by the formula C=l(.P. tan a,

it being a coefficient peculiar to the constructive characteristics of the pump.

Thus, in order to have a constant torque, it is necessary to cause or to vary so that the product P. tan a remains constant: this is possible, because of the spring 23, which is a spring having variable rigidity.

in practice, the curve which is characteristic of the spring 2d is determined experimentally. For this purpose, there is established experimentally for each value of the angle a, the pressure P which is necessary in order to have the required value of the torque C; it is then possible to determine, point by point, the law of increase of P as a function of tan a.

From this is deduced the calibration of the spring 24 which is necessary at each pressure P in order to obtain the corresponding angle a.

in this way, the characteristic curve of the spring 24 is obtained.

in the example which is described, the spring 24 has been represented as a band spring with variable spiral pitch, but it is quite evident that the invention is not limited to this particular embodiment and that the spring 24 can be formed by any other equivalent means, for example, by an assembly of springs which become operative in succession.

Thus, with each increase in the pressure P, the angle a of the plate is reduced by a determined quantity due to the calibration of the spring 24.

If the pressure P decreases, the valve member 27 uncovers the orifice 33. The pressure obtaining in the bore 26 decreases, and this more especially as the flow passing through the calibrated passage 18 is large, and this brakes the movement of the valve member 27 in a manner similar to that which has been previously described. The pressure acting on the piston 12, being always the same fraction of the delivery pressure, decreases and the pistons 3 force back the plate 9.

With the product of P X tan a remaining constant, P increases as tan a decreases, this being so, at least theoretically, until P tends towards infinity when tan tends towards zero; it is quite evident that if nothing is provided for limiting the maximum value of P, this latter can reach values such that the jacks or conduits will split or will be seriously damaged.

in order to limit the maximum value of P, a safety valve 36 is arranged in the pump. This valve comprises a valve member 37 which is subjected on one of its faces to the pressure P and is supported at its other face by a ring 38, having a predetermined calibration as a function of the maximum value which P can reach.

The valve 36 communicates at one end with the passages 35 and 3S and at the other end with a passage 33. This passage 39 ends in an annular chamber 40, surrounding the valve 36, this annular chamber communicating with a bore 41 which, through a nonretum valve 42, communicates by way of a passage 43 with one of the bores 4.

During half a revolution of the plate 9, the pressure obtaining at 43 is the intake pressure, and during the other half revolution, it is the pressure P; the annular chamber 40 thus receives a pulsatory premure equal to P.

When the pressure P exceeds a predetermined value, it lifts the valve member 37, thereby compressing the spring; the valve member 37 closes the passage 35 and then brings the passages 35' and 39 into communication, so that the piston 12 advances continuously in steps until the angle a is equal to zero, in which position the pump no longer delivers.

it is to be noted that, preferably, as shown in FIG. 2, the pump comprises an odd number 2n+l of pistons 3 a. The effect of this is that the pressure obtaining in the cylinder ll and acting on the piston 12 sometimes balances r: pistons and sometimes n+1 pistons; as with each revolutions the change from n pistons to n+1 pistons takes place 4n+2 times, if the pump is rotating at l5 revolutions per second, the pressure acting on the piston 12 and on the valve member 27 oscillates imperceptibly at a frequency of 150 c./sec. for a 5-piston pump, this having the effect of suppressing the friction threshold of the valve, which is thus extremely sensitive.

lclaim:

l. A hydraulic pump comprising:

a housing assembly having input and output orifices;

a support rotatable about a predetemtined axis;

a swashplate of variable inclination pivotally mounted on said support and rotatable about said predetermined axis;

a hydraulic control piston mounted within the support for modifying the inclination of said swashplate;

a regulating valve in fluid communication with said outlet orifice and coaxially located with respect to said axis;

said fluid communication enabling movement of said regulating valve in a direction along said predetermined axis;

a calibrated orifice assembly located in adjacent relationship with said swashplate;

a spring bearing located between said regulating valve and said calibrated orifice assembly for enabling inclination of said swashplate in accordance with the pressure at said outlet orifice to maintain a substantially constant driving torque for said pump; and said calibrated orifice assembly cooperating with sard spring bearing to determine forces acting against said regulating valve in a direction along said predetermined axis.

2. A pump as in claim 1 wherein said regulating valve receives on one of its faces the outlet pressure of said pump and on another face the combined action of said spring bearing and an intermediate hydraulic pressure inferior to said outlet pressure and which is a function of said outlet pressure and of the hydraulic flow going to or coming from said control piston.

3. A hydraulic pump according to claim 2 in which said intermediate pressure prevails in an intermediate chamber communicating with the control piston acting on the plate by way of a calibrated opening in said orifice assembly and in such a way that the pressure obtained in the chamber is a function of the speed of displacement of the said control piston, said pressure thus having a corrective action on the displacement of said regulating valve.

3. A hydraulic pump according to claim 2 for use with a reservoir tank in which said regulating valve comprises a valve member which causes said intermediate chamber to communicate either with the outlet pressure or with the tank, depending on its direction of movement.

5. A hydraulic pump according to claim 2 in which said spring bearing acting upon said regulating valve is located within said intermediate chamber.

6. A hydraulic pump according to claim 2 in which said spring bearing is a spring having a variable resiliency.

7. A hydraulic pump according to claim 6 in which the resilient characteristics of said spring hearing are determined so that a distinct angle a of the plate with said axis corresponds to each outlet pressure P, and thus the driving torque of the pump remains constant.

8. A hydraulic pump according to claim 2 further including an odd number of first pistons located to successively subject the swashplate to the action of a variable number of said first pistons to cause a pressure pulsation which suppresses the friction threshold.

9. A hydraulic pump according to claim 8 comprising: a calibrated spring and a safety valve having a valve member held in a neutral position by said calibrated spring, said valve member causing said intermediate chamber to communicate with the outlet of one of said first pistons of the pump when the pressure exceeds a predetermined valve, so that as soon as this pressure is reached, the control piston of the swashplate acts on this latter in order to bring the said angle a back to zero. 

1. A hydraulic pump comprising: a housing assembly having input and output orifices; a support rotatable about a predetermined axis; a swashplate of variable inclination pivotally mounted on said support and rotatable about said predetermined axis; a hydraulic control piston mounted within the support for modifying the inclination of said swashplate; a regulating valve in fluid communication with said outlet orifice and coaxially located with respect to said axis; said fluid communication enabling movement of said regulating valve in a direction along said predetermined axis; a calibrated orifice assembly located in adjacent relationship with said swashplate; a spring bearing located between said regulating valve and said calibrated orifice assembly for enabling inclination of said swashplate in accordance with the pressure at said outlet orifice to maintain a substantially constant driving torque for said pump; and said calibrated orifice assembly cooperating with said spring bearing to determine forces acting against said regulating valve in a direction along said predetermined axis.
 2. A pump as in claim 1 wherein said regulating valve receives on one of its faces the outlet pressure of said pump and on another face the combined action of said spring bearing and an intermediate hydraulic pressure inferior to said outlet pressure and which is a function of said outlet pressure and of the hydraulic flow going to or coming from said control piston.
 3. A hydraulic pump according to claim 2 in which said intermediate pressure prevails in an intermediate chamber communicating with the control piston acting on the plate by way of a calibrated opening in said orifice assembly and in such a way that the pressure obtained in the chamber is a function of the speed of displacement of the said control piston, said pressure thus having a corrective action on the displacement of said regulating valve.
 3. A hydraulic pump according to claim 2 for use with a reservoir tank in which said regulating valve comprises a valve member which causes said intermediate chamber to communicate either with the outlet pressure or with the tank, depending on its direction of movement.
 5. A hydraulic pump according to claim 2 in which said spring bearing acting upon said regulating valve is located within said intermediate chamber.
 6. A hydraulic pump according to claim 2 in which said spring bearing is a spring having a variable resiliency.
 7. A hydraulic pump according to claim 6 in which the resilient characteristics of said spring bearing are determined so that a distinct angle Alpha of the plate with said axis corresponds to each outlet pressure P, and thus the driving torque of the pump remains constant.
 8. A hydraulic pump according to claim 2 further including an odd number of first pistons located to successively subject the swashplate to the action of a variable number of said first pistons to cause a pressure pulsation which suppresses the friction threshold.
 9. A hydraulic pump according to claim 8 comprising: a calibrated spring and a safety valve having a valve member held in a neutral position by said calibrated spring, said valve member causing said intermediate chamber to communicate with the outlet of one of said first pistons of the pump when the pressure exceeds a predetermined valve, so thaT as soon as this pressure is reached, the control piston of the swashplate acts on this latter in order to bring the said angle Alpha back to zero. 